As a traveling speed of a vehicle has been becoming higher, durability of a pneumatic tire, which is mounted on the vehicle, and which is rotated at a high speed (hereinafter, high speed durability), has become more important than ever.
As to methods of enhancing high speed durability of a pneumatic tire, various proposals have so far been made (such as Japanese Unexamined Patent Application Publication Nos. Sho 62-251202, Hei 6-247103 and 2003-231405).
For example, in Japanese Unexamined Patent Application Publication No. Sho 62-251202, proposed is a method in which a ribbon-shaped layer member formed of cords made of polyamide-based organic fibers is provided all over the entire circumference of a shoulder portion of a pneumatic tire.
According to such a method, even in a case where a large centrifugal force occurs as the pneumatic tire is rotated at a high speed, a tread portion and the like of the pneumatic tire are restrained from expanding outward in a tire radial direction. For this reason, high speed durability of the pneumatic tire is enhanced.
That is, generally, by increasing the number of layers each configured of a layer member provided to a shoulder portion is increased, the high speed durability itself can be further enhanced.
On the other hand, in order to make a shape of the tread portion contacting with a road surface which is the same as that of a carcass line, it is necessary to keep a cross-sectional shape, in a tread width direction, of an outer surface of the tread portion contacting with a road surface to be the same as that of the carcass line. That is, there is the following problem. When the number of layers each configured of the layer member provided to a shoulder portion is increased, a tread gauge (the thickness of a tread rubber) of the shoulder portion becomes thinner than that of a center portion, and a wear life of the shoulder portion is reduced.
The present invention was made in consideration of such a problem, and aims to provide a pneumatic tire whose high speed durability is further enhanced without reducing a wear life of a shoulder portion thereof.